In electrohydraulic systems that include a plurality of electrohydraulic devices, such as valve-controlled actuators, pumps and motors, it is conventional practice to couple such devices to a remote master controller for coordinating device operation to perform desired tasks. Motors and actuators may be employed, for example, at several coordinated stages of a machine tool line for automated transfer and machining of parts at a series of work stations. In another typical application, the moving components of a man-lift platform may be coupled to electrohydraulic actuators controlled by a master controller on the platform responsive to operator lever or joystick inputs. In accordance with conventional practice, the master controller is coupled through individual digital-to-analog converters to the various remotely-positioned electrohydraulic devices for supplying control signals thereto. For closed-loop operation, a sensor is positioned at each electrohydraulic device for sensing operation thereof, and feeds a corresponding sensor signal to the remote master controller through an analog-to-digital converter or appropriate signal conditioner.
U.S. Pat. No. 4,744,218 (V-3939) and U.S. Application Ser. No. 164,958, filed Mar. 7, 1988 and assigned to the assignee hereof (V-4095), disclose electrohydraulic control systems in which a plurality of electrohydraulic devices are connected in common to a remote master controller by a high-speed serial communication bus. This electrohydraulic bus technique addresses and overcomes problems theretofore extant in the art as outlined in the preceding paragraph. However, it has been found that some applications of the bus technique require electrical isolation of one or more controllers from earth ground. For example, in man-lift platform applications of the type previously described, it is desirable to isolate the master controller on the platform from electrical ground for use in conjunction with high-voltage power lines and the like. It is therefore an object of the present invention to provide an improved communication system, having particular utility in bussed electrohydraulic control systems of the described character, that includes facility for electrically isolating one or more controllers from each other and from electrical ground.